The present invention relates to a vacuum molding process and apparatus which utilizes a flexible molding cover or bag to place a vacuum onto a container filled with an uncured cement mixture.
In the past, it has been common to mold various types of products out of a cement or concrete which includes the making of a mixture of a predetermined Portland cement which may include the addition of gravel or lightweight components, such as polymer beads or the like. The mixture is typically cured by mixing a predetermined amount of water with the cement mixture and mixed in a mixer which may be a cement truck with a rotating mixer. Typically in a molding operation, the cement is mixed at the location of the molding operation and the mixed cement is placed in the mold and cured to form a predetermined molded product. The product can include sculptures, containers, balustrades, or other building components and can be molded with standard cement or concrete mixture or lightweight concrete having lightweight particles incorporated into the cement to reduce the weight of the molded product.
It has been suggested in the past to vibrate the mold once the cement or other molding material has been placed therein to get entrained air or other gases out of the cement material to remove air pockets and bubbles from the molded product. This is commonly done by placing the filled mold with the uncured mixed cement onto a vibrating table in which the vibration causing the bubbles to rise in the cement to thereby make a sounder molded product. It has also been suggested to attach a vibrator clamp to a mold and a vibrator to the clamp to vibrate the mold during the molding operation to remove gases and to compact the molded mixture. A centrifugal molding or casting machines have been used which result in the rapid rotation of the mold loaded with a molding material. Another method of removing bubbles is to place the mold on a vacuum chamber or the like and place a vacuum on the area around the mold for withdrawing bubbles from the mold.
In contrast to these prior art systems, the present invention uses an ordinary flexible plastic film which may be reinforced with crinkling or with fibers and in which a vacuum pump is connected thereto through a vacuum hose. The plastic sheet material can be rigid or flexible transparent or opaque and formed in such a fashion that would be concave and conform with the flow of vacuum. The plastic film is easily clamped over conventional containers, such as a wheelbarrow or mixing container, with a sealing clamp and may also include a vacuum bag for placing over a mold. The mold can be placed on a vibrating table or having a vibrating clamp attached thereto with a vibrator for vibrating the mold in a partial vacuum for the removal of gas bubbles from the molded material.
One prior art U.S. patent can be seen in the Lee patent, U.S. Pat. No. 4,990,082, for a vibrator with suction apparatus which illustrates a vibrator for architectural or civil engineering and uses a reciprocating or rotating vibrator along with a suction system which is integrally formed with the vibrating means and has at least one suction member to be attached to the forming mold. The suction system is such to enable an airtight connection between the vibrator and the forming molds and is substantially in the shape of a disc with an air passage formed therein to operate with an air pump to produce a low pressure area in the disc body. The Gayso patent, U.S. Pat. No. 4,796,686, is a centrifugal casting machine with venturi actuated vacuum venting. A centrifugal force casting machine develops a vacuum as it travels through the air on the spinning arms of a casting machine in order to evacuate unwanted gases from the casting mold. The Abbott patent, U.S. Pat. No. 3,323,188, is an apparatus for molding and compacting hollow concrete products including a pulsating water vibrator. The Emmons patent, U.S. Pat. No. 2,610,040, is an operating mechanism for a vibrating table used in molding a product. The Dubbs et al. patent, U.S. Pat. No. 2,603,850, is a method and apparatus for molding concrete products. The Lake patent, U.S. Pat. No. 2,386,961, is another apparatus for molding tubular concrete products which utilizes both pressure and a vacuum in connection with the molding of the product.
The present application includes a suction apparatus which uses a flexible plastic film which may be in the form of a plastic bag or a plastic cover which can be placed over conventional or nonconventional containers, such as placing the mold in a plastic bag and sealing the opening to the bag. A plastic film, such as sold by Film Technology, Inc. under U.S. Pat. No. 5,129,813, can be used in the present invention. A vacuum is then placed in the area under the cover to place a vacuum on the uncured cement mixture in the container or mold which consists in the removal of bubbles and may also include a means for simultaneously vibrating the mold or cement mixture. The system can be made to fit a wide variety of different molds as well as molding operations and unusual containers.